1. Field of the Invention
The present invention relates to a method for fabricating a capacitor of a semiconductor device, and more particularly, to a method for forming a lower electrode structure of a capacitor, wherein a metal such as titanium is reacted with the upper portion of a polysilicon plug connected to the substrate through an insulation layer, to form a silicide contact for electrical contact with the lower electrode.
2. Description of the Background Art
Any capacitor, such as that used for a memory cell of a semiconductor device, basically includes a pair of electrodes separated by a dielectric layer. In a semiconductor device comprising a gate, source, and drain, the lower electrode is connected to an active region of the device through a contact hole.
In the development of memory devices having increased memory capacity, an increased cell capacitance must be secured for ever-diminishing areas. In order to obtain increased cell capacitance within a given area, one of three conditions should be satisfied:
the dielectric layer should have an increased dielectric constant, either by way of dielectric material selection or by subsequent processing of the dielectric layer, e.g., by a thermal treatment process; the effective area between the plates (electrodes) should increased in some manner, for example, by utilizing a three-dimensional dimensional electrode structure; or the capacitor should be fabricated such that the distance between the plates is decreased, meaning that the dielectric layer is made thinner. There is a practical limit to decreasing the thickness of the dielectric layer, and three-dimensional structures are highly complex formations, which have their own limitations.
As one example of the aforementioned thermal treatment process to improve the dielectric layer, an oxide annealing process may be performed at a high temperature of approximately 700.degree. C. to enhance properties of the dielectric layer. Such a process, however, also produces an undesirable oxidation effect, i.e., a natural oxide film grows on the electrode surfaces, which causes a reduction in the resultant capacitance. The oxidation of conductive surfaces occurs due to oxide gases reaching the lower electrode by seeping under the dielectric layer, in particular, at the edges thereof.
Meanwhile, in coping with the tendency for the contact hole to have a higher aspect ratio due to decreased areas (hole size) in more highly integrated semiconductor devices, in many cases, the capacitor needs to be provided with a conductive plug for connecting the active region and the lower electrode. The plug is formed by filling the contact hole, which is formed in a relatively thick insulation layer, with a doped polysilicon, thus establishing an interface for electrical connection between the upper surface of the plug and the lower surface of the lower electrode.
However, in such a capacitor, i.e., one having such a plug, the plug interface may become oxidized during the above thermal treatment process, which degrades the adhesive force between the lower electrode and the plug, especially in the event of imperfect alignment conditions between the polysilicon plug and the lower electrode. This degraded adhesion causes a lifting phenomenon, whereby the plug may become separated from the lower electrode during subsequent processing. Such separation reduces the overall capacitance and degrades the electrical characteristics of the capacitor, such as leakage current and reliability, while decreasing the yield rate of a semiconductor device having such a capacitor.